A brake is mainly composed of a brake unit and a thruster or a thrust device. A “Variable-Force Thruster For Brake” is disclosed in patent publication No. CN2937582 (the application number is 200620050535.0) published on Aug. 22, 2007, in which the thruster is hinge-connected with a drive arm in the brake unit via a push lever of the thruster to act on the brake unit, so that the brake unit is brought into an operating state. The thruster comprises a drive device, a liquid pump driven by the drive device, a liquid accumulator, and a hydraulic cylinder. The inlet of the liquid pump is communicated with the liquid accumulator, the outlet of the liquid pump is communicated with the drive liquid cavity of the hydraulic cylinder, and the non-drive liquid cavity of the hydraulic cylinder is communicated with the liquid accumulator. In a case of being applied to a normally closed braking, the push lever of the thruster extends out to a predetermined position to release braking in the normally closed state; and when the push lever is retracted, i.e., restoring the normally closed braking of the brake unit, the thruster only enables the brake unit to generate one-time braking of restoring the normally-closed state during the operation of braking.